Method for programming and erasing non-volatile memory with nitride tunneling layer

ABSTRACT

A method for programming and erasing a non-volatile memory with a nitride tunneling layer is described. The non-volatile memory is programmed by applying a first voltage to the gate and grounding the substrate to turn on a channel between the source and the drain, and applying a second voltage to the drain and grounding the source to induce a current in the channel and thereby to generate hot electrons therein. The hot electrons are injected into a charge-trapping layer of the non-volatile and trapped therein through the nitride tunneling layer. The non-volatile memory is erased by applying a first positive bias to the drain, applying a second positive bias to the gate, and grounding the source and the substrate to generate hot electron holes in the channel region. The hot electron holes are injected into the charge-trapping layer through the nitride tunneling layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of, and claims the prioritybenefit of, U.S. application Ser. No. 10/015,414 filed on Dec. 12, 2001.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a method for programming and erasing anon-volatile memory. More particularly, the present invention relates toa method for programming and erasing a non-volatile memory with anitride tunneling layer.

2. Description of Related Art

The family of the non-volatile memory includes the erasable programmableread-only memory (EPROM) and the electrically erasable programmableread-only memory (E²PROM). Particularly, the E²PROM can be erased andprogrammed electrically and is capable of retaining data even if thepower is turned off, and therefore is widely used in personal computersand in electronic apparatuses.

The E²PROM with a silicon oxide/silicon nitride/silicon oxide (ONO)stacked structure is recently developed, which includes theSilicon-Oxide-Nitride-Oxide-Silicon (SONOS) memory and the nitrideread-only memory (NROM). By comparing with the conventional non-volatilememory having a doped polysilicon floating gate, the SONOS memory useslower voltages for its operation and therefore can be easily scaled downfor a higher integration. On the other hand, the NROM is able to preventa leakage and to store two bits in one memory cell, and therefore has abetter performance. A typical NROM is capable of preventing a leakage isbecause the injected electrons are localized in certain regions in thesilicon nitride charge trapping layer. These injected electrons are lesslikely to locate on the defects in the tunnel oxide layer that wouldotherwise cause a leakage.

However, since the SONOS memory and the NROM both use silicon oxide asthe material of the tunneling layer, the following problems areencountered.

Since silicon oxide has a high energy barrier for an electron and anelectron hole, the efficiency of hot carrier (electron or electron hole)injection through the tunnel oxide layer is low when the channel hotcarrier injection mechanism is used to program or to erase the SONOS orNROM device. Thus the rates of the programming operation and the erasingoperation of the memory device are lowered.

SUMMARY OF THE INVENTION

Accordingly, this invention provides a method for programming anderasing a non-volatile memory with a nitride tunneling layer, which canpromote the efficiency of a programming operation or an erasingoperation of a memory device.

The method for programming a non-volatile memory with a nitridetunneling layer of this invention comprises the following steps. Thegate of the non-volatile memory is applied with a first voltage and thesubstrate is grounded to turn on the channel between the source and thedrain. The drain is applied with a second voltage and the source isgrounded to induce a current in a channel and thereby generate hotelectrons therein. The hot electrons are injected into a charge-trappinglayer of the non-volatile memory and trapped therein through the nitridetunneling layer.

The method for erasing a non-volatile memory with a nitride tunnelinglayer of this invention comprises the following steps. The drain isapplied with a first positive bias, the gate is applied with a secondpositive bias, and the substrate and the source are both grounded togenerate hot electron holes in the channel region. The hot electronholes are injected into the charge-trapping layer through the nitridetunneling layer and are recombined with the electrons therein tocomplete the erasing operation.

Moreover, in the method for programming and erasing a non-volatilememory with a nitride tunneling layer of this invention, the firstvoltage, the second voltage, the first positive bias, and the secondpositive bias mentioned above are all lower than those used in theoperation of the SONOS memory of the same size.

Since the tunneling layer in this invention is made from silicon nitridethat has a energy barrier lower than that of silicon oxide used in theprior art, the efficiency of the channel hot carrier injection can bepromoted and the operating rates of the memory device are thusincreased.

Besides, since the dielectric constant of silicon nitride is higher thanthat of silicon oxide, lower operating voltages can be used to programor to erase the non-volatile memory with a nitride tunneling layer.Therefore, the critical dimension and the size of a memory cell can befurther reduced for a higher integration.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 schematically illustrates a non-volatile memory with a nitridetunneling layer according to a preferred embodiment of this invention ina cross-sectional view;

FIG. 2 schematically illustrates the method for programming anon-volatile memory with a nitride tunneling layer according to thepreferred embodiment of this invention; and

FIG. 3 schematically illustrates the method for erasing a non-volatilememory with a nitride tunneling layer according to the preferredembodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a non-volatile memory with a nitridetunneling layer according to a preferred embodiment of this invention ina cross-sectional view.

Refer to FIG. 1, the non-volatile memory with a nitride tunneling layercomprises a substrate 100, a nitride tunneling layer 102, acharge-trapping layer 104, a dielectric layer 106, a gate conductivelayer 108, a source region 112, a drain region 114, and a channel region116.

The substrate 100 comprises, for example, silicon. The substrate 100 isof n-type (p-type) when the non-volatile memory to be formed is ap-channel (n-channel) memory.

The nitride tunneling layer 102 is disposed on the substrate 100. Thenitride tunneling layer 102 is formed by, for example, chemical vapordeposition (CVD).

The charge-trapping layer 104 is disposed on the nitride tunneling layer102. The material of the charge-trapping layer 104 a is, for example,silicon nitride and the method for forming the charge-trapping layer 104a is, for example, chemical vapor deposition (CVD).

The dielectric layer 106 is formed on the charge-trapping layer 104. Thedielectric layer 106 is formed from, for example, silicon oxide and isformed by, for example, chemical vapor deposition (CVD).

The gate conductive layer 108 is disposed on the dielectric layer 106.The gate conductive layer 108 comprises, for example, polysilicon and isformed by a method such as chemical vapor deposition. Besides, the gateconductive layer 108, the nitride tunneling layer 102, thecharge-trapping layer 104, and the dielectric layer 106 togetherconstruct a stacked gate structure 110.

The source region 112 and the drain region 114 are formed in thesubstrate 100 beside the gate structure 110. The source/drain region112/114 has a conductive type different from that of the substrate 100,i.e., the source/drain region 112/114 is of p-type (n-type) when thesubstrate 100 is of n-type (p-type).

The channel region 116 is located in the substrate 100 under the gatestructure 110 and between the source region 112 and the drain region114.

FIG. 2 schematically illustrates the method for programming anon-volatile memory with a nitride tunneling layer according to thepreferred embodiment of this invention.

Refer to FIG. 2, when the non-volatile memory with a nitride tunnelinglayer is to be programmed, the gate 110 is applied with a first voltageV₁ and the substrate 100 is grounded to turn on the channel 116 betweenthe source 112 and the drain 114, wherein the first voltage V₁ rangesfrom about 6V to about 12V. Meanwhile, the drain region 114 is appliedwith a second voltage V₂ ranging from about 2.5V to about 5V and thesource region 112 is grounded to induce a current 118 in the channelregion 116 and thereby generate hot electrons. The hot electrons areinjected into the charge-trapping layer 104 through the nitridetunneling layer 102 because of the attraction of the gate conductivelayer 108 at a higher voltage level.

FIG. 3 schematically illustrates the method for erasing a non-volatilememory with a nitride tunneling layer according to the preferredembodiment of this invention.

Refer to FIG. 3, when the non-volatile memory with a nitride tunnelinglayer is to be erased, the drain region 114 is applied with a firstpositive bias V_(B1), the gate conductive layer 108 is applied with asecond positive bias V_(B2), and the source region 112 and the substrate100 are both grounded to generate hot electron holes in the channelregion 116, wherein the first positive bias V_(B1) ranges from about 2Vto about 5V and the second positive bias V_(B2) ranges from about 2.5Vto about 5V. The hot electron holes are injected into thecharge-trapping layer 104 through the nitride tunneling layer 102.

Moreover, in the method for programming and erasing a non-volatilememory with a nitride tunneling layer according to the preferredembodiment of this invention, the first voltage V₁, the second voltageV₂, the first positive bias V_(B1), and the second positive bias V_(B2)mentioned above are all lower than those used in the operation of theSONOS memory of the same size.

Besides, since the dielectric constant of silicon nitride is higher thanthat of silicon oxide, lower operating voltages can be used to programor erase the non-volatile memory with a nitride tunneling layer.Therefore, the critical dimension and the size of a memory cell can befurther reduced for a higher integration.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncovers modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A method of programming a non-volatile memory cell with a nitridetunneling layer, comprising: providing a non-volatile memory cellcomprising: a substrate a nitride tunneling layer disposed on thesubstrate; a charge-trapping layer disposed on the nitride tunnelinglayer; a dielectric layer disposed on the charge trapping layer; a gateconductive layer disposed on the dielectric layer; and a source regionand a drain region disposed in the substrate adjacent to the nitridetunneling layer; applying a first voltage to the gate conductive layerand grounding the substrate to turn on a channel between the sourceregion and the drain region; and applying a second voltage to the drainregion and ground the source region to induce a current in the channeland thereby to generate hot electrons in the channel, wherein the hotelectrons are injected into the charge-trapping layer through thenitride tunneling layer to program the nonvolatile memory cell.
 2. Themethod of claim 1, wherein the first voltage ranges from about 6V toabout 12V.
 3. The method of claim 1, wherein the second voltage rangesfrom about 2.5V to about 5V.
 4. The method of claim 1, wherein the firstvoltage and the second voltage are both lower than those adopted forprogramming a substrate-oxide-nitride-oxide-silicon (SONOS) memoryhaving a same size as the non-volatile memory with the nitride tunnelinglayer.